1. Field of the Invention
The present invention relates to an ink jet print head that ejects ink onto a surface of a print medium to form an image and more particularly to an ink jet print head having a flexible film substrate mounted on a substrate formed with print elements to generate energy for ejecting ink.
2. Description of the Related Art
An ink jet printing system generally comprises an ink jet print head having nozzles or ejection openings to eject ink and a supply system to supply ink to the print head.
FIGS. 1 to 3 are perspective views showing a representative example of an ink jet print head. This construction basically can properly apply the present invention described later.
An ink jet print head H1000 generally comprises a print element unit H1002, an ink supply unit H1003 and a tank holder H2000. As shown in FIG. 3, the print element unit H1002 has a first print element substrate H1100, a second print element substrate H1101, a first plate H1200 used as a base, an electric wiring tape H1300 serving as a flexible wiring member, an electric contact substrate H2200, and a second plate H1400 for accommodating the print element substrates. These are assembled and mounted on the ink supply unit H1003. The ink supply unit H1003 has an ink supply member H1500, a flow path forming member H1600, a joint seal member H2300, a filter H1700 and a seal rubber H1800. These are assembled and accommodated in the tank holder H2000.
Here, the construction of the print element unit H1002 will be explained.
The print element unit H1002 is generally manufactured in the following processes.
Process 1: Forming a plate assembly by joining the first plate H1200 and the second plate H1400.
Process 2: Mounting two print element substrates H1100 and H1101 on the plate assembly.
Process 3: Positioning electrode terminals H1302 of the electric wiring tape H1300 and electrode portions of the print element substrates, and joining the electric wiring tape to the plate assembly.
Process 4: Connecting the electrode terminals H1302 of the electric wiring tape H1300 and the electrode portions of the print element substrates.
Process 5: Sealing the electrical connections.
Each of the above processes will be detailed in the following.
Process 1
The first plate H1200 is formed with ink supply ports H1201 to supply a black ink to the first print element substrate H1100 and cyan, magenta and yellow inks to the second print element substrate H1101. The second plate H1400 is joined to the first plate H1200 in a way that exposes the ink supply ports H1201. Where the ink supply ports H1201 are exposed, the second plate H1400 joined to the first plate H1200 is formed with device holes H1401 to accommodate the two print element substrates H1100, H1101.
Process 2
The first print element substrate H1100 and the second print element substrate H1101 are securely bonded with high precision to the exposed portions of the first plate H1200 through the device holes H1401. The positioning of the first and second print element substrates is made with respect to an X-direction positional reference surface H1204 and a Y-direction positional reference surface H1205 both formed in the first plate H1200. The print element substrates each having a plurality of ink ejection openings have a known construction employed in an ink jet print head.
Process 3
The electric wiring tape H1300 is a laminate of a base film, copper foil wires and a wire protecting cover film or solder resist. The base film may, for example, be formed of a polyimide resin to a thickness of about 25–125 μm. The copper foil wires have a thickness of 35 μm and are formed in a predetermined shape to connect the two print element substrates to the electric contact substrate H2200. Portions of the electric wiring tape H1300 that the print element substrates are built into, are formed with device holes H1304 of almost the same shape as the device holes H1401. At two sides of each of the device holes H1304 which correspond to the electrode portions of the print element substrates, electrode terminals H1302 plated with gold on their surface are arrayed as connection terminals. The electric wiring tape H1300 is secured on its cover film side to the surface of the second plate H1400 through a thermosetting epoxy resin bonding layer. The base film of the electric wiring tape H1300 is made smooth on its surface as it is engaged with a capping member of the print element unit.
Process 4
Electric connection between the electric wiring tape H1300 and the two print element substrates is made by performing an inner lead bonding (abbreviated ILB) on the electrode terminals H1302 of the electric wiring tape H1300 and bumps provided in advance on the electrode portions of the print element substrates, for example.
Process 5
When the electric connections are exposed after ILB, the electrode portions are covered and sealed with a sealant H1308 (FIG. 2) with excellent sealing and ion interruption capabilities, such as epoxy resin, because fine ink sprays flying from ejection openings or ink drops bouncing back from a print medium may adhere to the electrode portions, corroding the electrode portions and base metals. To form liquid-tight ink communication paths running from the ink supply ports H1201 to ejection openings H1107, the surrounding of each print element substrate and gaps between the print element substrates and the device holes are covered with a sealant H1307.
The sealant (first sealant) H1307 applied to the surroundings of the print element substrates is chosen to have a high fluidity and a high elasticity so that the sealant when hardened will not cause stresses such as hardening shrinkage to the print element substrate. The other sealant (second sealant) H1308 applied to the electric connections is chosen to have a high hardness to provide such properties as wear resistance against rubbing motions of a rubber wiper blade to wipe off ink drops adhering to an ejection opening forming face and durability against being flaked off should a print medium contact it.
Then, the electric terminal contact member H1303 on an electric input side of the electric wiring tape H1300 and the electric contact substrate H2200 to transfer electric signals from the printing apparatus body are connected together by, for instance, an ACF (Anisotropic Conductive Film) and the terminal connection portions are also covered with a sealant.
The print element unit H1002 assembled in the above processes and the ink supply unit H1003 are joined together through the joint seal member H2300. Screws H2400 are fastened into screw fixing bosses H1517 in the ink supply unit H1003 through screw setting positions H1207 provided in two screw setting portions H1206 of the first plate. At this time, the positional reference surfaces H1204, H1205 of the first plate and its back surface engage abutment portions H1509, H1510, H1511 of the ink supply unit H1003. This positions the print element unit H1002 in the X direction (main scan direction), Y direction (sub-scan direction) and Z direction (ink ejection direction). The electric contact substrate H2200 is positioned and fixed by a terminal positioning pins H1515 and terminal connecting pins H1516 of a terminal fixing portion H1512 of the ink supply unit H1003 coming into terminal positioning holes H1309 and terminal connecting holes H1310 of the electric contact substrate.
Then, the tank holder H2000 is mounted on the assembly of the print element unit H1002 and the ink supply unit H1003 to provide an ink jet print head H1000 of FIG. 1. When ink tanks (not shown) are installed in the tank holder H2000, ink is supplied from the filter H1700 of the ink supply unit H1003 into the ink paths H1501 in the flow path forming member H1600. Ink is further fed from an ink introducing port H1602 into the print element unit H1002.
Although the ink jet print head described above has a black ink ejection portion and a color ink ejection portion formed integral as one piece, the similar manufacturing process can also be applied to an ink jet print head with separate print element substrates for individual colors.
The ink jet print head, however, has the following problems that may degrade reliability.
As described above, the second sealant H1308 that covers the electric connections between the electric wiring tape H1300 and the print element substrates is hard and highly durable. Thus, where the second sealant H1308 is placed over the soft first sealant H1307, which seals the outer periphery of the print element substrates, may be cracked when applied a local external force as the first sealant H1307 deforms. From these cracks ink may seep in, leading to corrosion of electric connections.
To solve this problem, a method has been proposed (see Japanese Patent Application Laid-open No. 2002-187273) which involves extending the base film of the electric wiring tape H1300 at both ends of the arrays of the electrode terminals H1302 slightly into the device holes and applying the second sealant H1308 over the extension portions H1305 so as to cover the electric connections. This document also discloses that the extension portions H1305 may have a conductive layer to particularly enhance stiffness.